The invention relates to a cable, especially a submarine cable, with a cable core having at least one conductor and with armoring surrounding the cable core, which armoring has armoring wires, or with a cable core having at least one conductor and with armoring surrounding the latter and composed of a plurality of armor sections, which have armoring wires. The invention further relates to a method for the manufacture of a cable, especially a submarine cable, a continuous cable core being provided with at least one outer armoring.
In addition to a cable core having predominantly metal and/or optical conductors cables have armouring composed of one or more armour layers surrounding the said core. The armouring absorbs mechanical stresses acting on the cable. The armouring serves, particularly in the case of submarine cables, to protect the cable core with the conductors from the mechanical loads that occur when laying and taking up cables, bringing them ashore and burying them or the like. In ocean areas with rocky, dissected seabed in the region of underwater mountain ranges with steep inclines, and also in shallower waters used for fishing and for anchorage on the routes proposed for bringing cables ashore, submarine cables are protected by additional armour layers.
The armouring, particularly on submarine cables that are laid on routes with different depths of water and/or changing seabed formation, is not exposed to the same loading everywhere over the continuous length of the cable. Since the structure of the armouring on continuous submarine cables has always to be designed as a function of the maximum load, however, the armouring is overdimensioned on longitudinal sections subject to less loading.
Forming cables, and in particular submarine cables, from assembled cable sections that have one or more armour layers depending on the loading in order to adapt to different mechanical loads is already known. For this purpose the cable sections of differing structure must be joined to one another at their opposing ends. This is done by means of additional jointing sleeves or splices between the adjoining ends of differently structured cable sections.
Proceeding from this, the object of the invention is to create a cable, in particular a submarine cable, which has a structure suited to the local requirements. Another object of the invention is to create a simple method for the manufacture of such a cable, in particular a submarine cable.
A cable for achieving the stated object has the characteristic features of a continuous cable core having at least one conductor and with armouring surrounding the cable core. Owing to the fact that individual armouring wires are replaced, at least in some areas, by filler strands composed of a less tensile and/or flexurally lax material, especially lighter material, an armouring can be created, which if adapted to the prevailing mechanical loads acting on the cable. The filler strands here serve practically only as gap fillers, which ensure that the armouring remains closed all around.
Owing to the fact that a greater or lesser number of armouring wires is replaced, as necessary, by filler strands in the longitudinal direction of the cable, the cable has armouring of differing load-bearing capacity along its length, which can be located to suit requirements by replacing a certain number of armouring wires with filler strands, section by section where fewer loads are exerted on the armouring. The filler strands do not absorb any significant mechanical loads. The possibility of forming the filler strands from a less tensile and/or flexurally lax material makes the cable lighter and less expensive.
The principle according to the invention of replacing the armouring wires by filler strands, as required, can be employed not only on submarine cables but on all conceivable types of cable and cable structures. At the same time the individual armouring wires and filler strands in the armouring may either run rectilinearly in the longitudinal direction of the cable, or be twisted and/or stranded.
A further cable for achieving the aforementioned object has the features of a continuous cable core having at least one conductor, with armouring surrounding the cable, and being composed of a plurality of amour sections. According to this the cable in the area of the armouring is formed from more than one and at least two armour sections, the cable core at least, however, being uninterrupted. The armouring of an armour section has at least one filler strand in at least one end area, which strand replaces a section of an armouring wire in the relevant end area of the armour section. Replacing one or even more armouring wires in the end area of at least one armour section with filler strands reduces the mechanical, external load bearing capacity of the relevant area of the cable towards the end of the armour section affected. All armouring wires of an armour layer of the armour section are preferably replaced by filler strands towards at least one end. At the end of such an armour section at least one outer armour layer then only has filler strands.
The armour sections suitably have different armouring for adapting the cable to different external loads. This applies in particular to submarine cables, which are laid, for example, at different depths and/or on seabeds of differing consistency (formation) In such a case the armour sections to be joined usually have a different number of armour layers. For example, an area of the cable subject to less loading has only a single armour layer, while an area subject to heavier loading has two (or even more) armour layers. In this case the outer armour layer of the armour section having more than one armour layer will preferably have a number of armouring wires diminishing in the longitudinal direction towards the end in the direction of the other armour section. Replacing these armouring wires by filler strands of preferably identical cross section means that the filler strands increase towards the end of the relevant armour section, possibly to such an extent that at the end of the armour section the outer armour layer only has filler strands. Due to the fact that the cross sections of the filler strands preferably correspond to those of the armouring wires, the external armour layer remains closed.
It is further proposed to join the filler strands replacing the armouring wires in certain sections to the respective armouring wire in the course of the respective cable, especially the uninterrupted cable core. The armouring wire that is removed in certain areas is thereby continued, that is to say extended in the longitudinal direction of the cable by the filler strand serving as spacer. The respective armouring wire is joined to the filler strand in particular by means that do not result in significant thickening of the joint. For example, a thin-walled tube is used. Bonding the opposing ends of the armouring wire and of the filler strand together is also feasible however.
A method for achieving the aforementioned object in which the armouring is formed from different armour sections. Due to the fact that the continuous cable core is provided with armouring, which is formed from different armour sections, armouring can be formed that is suited to the requirements. Where the mechanical loads on the cable are smaller, because a submarine cable is laid at shallower depths and buried, for example, an armour section with a smaller number of armouring wires can be used. In areas subjected to greater loads on the other hand, the armouring has the armour sections with a larger number of armouring wires. A cable, in particular submarine cable, can thus be formed, which has armouring of differing load bearing capacity in different areas. In the case of submarine cables the armour sections are suitably selected and located so as to produce armouring suited to the prevailing requirements, the armouring on submarine cables in particular being adapted to the depth-profile of the cable route.
Due to the fact that sections of at least some armouring wires or whole armouring wires of at least one selected armour section are replaced by filler strands and the filler strands are joined to armouring wires of another armour section or those armouring wires, sections of which are replaced and filled by the filler strands, any length and number of heavier and more rigid armouring wires can be replaced, as necessary, by lighter and in particular flexurally lax filler strands. At the same time the filler strands fill the spaces left by the replaced sections of the armouring wires in the relevant armour layer and hold the remaining armouring wires in the armour layer together. The armouring wires with the filler wires thereby form an altogether closed armour layer, so that the manufactured cable retains its shape.
According to a preferred development of the method the armouring wires, preferably of an outer armour layer, are increasingly replaced by filler strands towards the end of the respective armour section, to such an extent that at the end of an armour section at least the outer armour layer has only filler strands, which may possibly overlap the single (inner) armouring of the adjoining armour section by a short distance. By virtue of their flexurally lax characteristics, the filler strands exclusively present in the outer armour layer at the end of the relevant armour section guarantee cohesion of the outer armour layer at the end of the armour section, so that the filler strands of the outer armour layer do not burst open.
The ends of the filler strands of the outer armour layer are preferably held together by a binding band, for example a wrapping composed of high-tensile fibers preferably over the entire transitional area between adjacent armour sections, In order to form a continuous transition the said binding band or wrapping may extend over the adjoining end area of the adjacent armour section that has a smaller cross section owing to the absence of an armour layer.